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Abstract:

An anode active-material for rechargeable lithium batteries and methods
of manufacturing the same. This includes preparing an anode
active-material for rechargeable lithium batteries, including
heat-treating a mixture of Li2CO3, MnO2, MgO,
Al2O3 and Co3O4 at 900-1000° C. in air or
oxygen for 10-48 hours, generating a lithium-containing oxide; generating
metal-oxide nanoparticles MO (5-500 nm) (M represents Mg, Co or Ni, with
a valence of 2); and dry or wet mixing 0.01-10 wt % of pulverized metal
oxide nanoparticles with the lithium-containing oxide to form an anode
active-material. Spinel type MgAl2O4 is substituted into a
basic spinel-structure (Li1.1Mn1.9O4) for structural
stability. Spinel type Co3O4 is substituted to improve
electronic conductivity, improving battery performance. Metal-oxide
nanoparticles (5-500 nm) act as scavengers of HF generated by electrolyte
decomposition, wherein the spinel type anode active-material may be used
as an anode active-material of spinel type LiMn2O4 for
rechargeable lithium ion batteries, realizing low-price, high-output,
long-lifespan and high-capacity.

2. The anode active material of claim 1, wherein the spinel type anode
active material is mixed with metal oxide nanoparticles MO (5 to 500 nm)
(where M represents one of Mg, Co and Ni, and has a valence of 2).

3. The anode active material of claim 2, wherein the metal oxide
nanoparticles MO act as scavengers of HF generated by decomposition of an
electrolyte.

4. The anode active material of claim 2, wherein the metal oxide
nanoparticles are mixed in an amount of 0.01 to 10 wt % with the spinel
type anode active material.

Description:

TECHNICAL FIELD

[0001] The present invention relates to an anode active material for
rechargeable lithium batteries and a method of manufacturing the same.
More particularly, the present invention relates to an anode active
material for rechargeable lithium batteries, which exhibits excellent
electrochemical characteristics and thermal stability.

BACKGROUND ART

[0002] Recently, with the development of portable electronic devices
including mobile phones, notebook computers, and the like, along with the
commercialization of electric vehicles and hybrid electric vehicles, the
need for high capacity rechargeable batteries has rapidly increased.
Particularly, since performance of such electric devices mainly depends
on rechargeable batteries, there is high demand for high performance
batteries.

[0003] A rechargeable battery is generally composed of a cathode, an
anode, an electrolyte, and the like, and an anode active material is an
essential component for supplying lithium ions in the battery. The anode
active material serves to supply lithium cations to a cathode through
electrochemical reaction and the development of anode active materials is
known to be more difficult than that of cathode active materials. As a
raw material for the anode active materials, lithium cobalt oxide
(LiCoO2) is generally used in the art, but can affect cycle life of
the lithium battery through phase change in a high voltage region during
operation cycle of the battery (J. Electrochem. Soc., 139 (1992), 2091).

[0004] Although LiNi0.8Co0.15Al0.05O2, which has
higher capacity than LiCoO2, is also receiving attention,
LiNi0.8Co0.15Al0.05O2 active materials suffer from
violent price fluctuation associated with the price instability of
nickel. In particular, LiNi0.8Co0.15Al0.05O2 causes
explosion of the battery due to thermal instability in a charged state
(Electrochem. Solid State Lett. 7, A380-A383 (2004)).

[0005] As a result, manganese-based materials have received attention as
an alternative material in view of stable supply of inexpensive raw
materials, no toxicity, and electrochemical and thermal stability. In
particular, lithium manganese oxides of a spinel structure, including
LiMnO2, Li4Mn5O12, Li2Mn4O9,
LiMn2O4, and Li1.1Mn1.9O4, have attracted. In
particular, Li[(Ni0.5Mn0.5)1-xCox]O2
(0≦x≦0.5) having excellent thermal stability is a strong
candidate for next generation high output and large capacity rechargeable
lithium batteries.

[0006] Li[(Ni0.5Mn0.5)1-xCox]O2 exhibits
relatively high capacity and excellent reversibility. However, since
Li[(Ni0.5Mn0.5)1-xCox]O2 has a smaller amount of
Co serving to increase electron conductivity of the material per se than
LiCoO2, Li[(Ni0.5Mn0.5)1-xCox]O2 has
unsatisfactory rate capability. In addition, since thermal instability of
Li[(Ni0.5Mn0.5)1-xCox]O2 in a charged state is not
overcome (Journal of the Electrochemical Society, 155, A374-A383 (2008)),
applicability of Li[(Ni0.5Mn0.5)1-xCox]O2 to high
output and large capacity battery systems is not sufficiently
ascertained.

[0007] LiMn2O4 has been studied as an anode active material
since it has a spinel structure and exhibits high operating voltage and
relatively high reversible capacity. This material employs manganese,
which is present in high concentration in the earth's crust, and thus is
much cheaper than other active materials. Since this material has
slightly lower reversible capacity than LiCoO2 and LiNiO2,
there is a difficulty in using this material as an anode active material
for a rechargeable lithium ion battery of a portable power source.
However, LiMn2O4 has excellent thermal stability as compared
with other anode active materials. For this reason, it is expected that
LiMn2O4 will be applied to an anode active material for medium
and large rechargeable lithium ion batteries due to stability thereof.

[0008] However, although LiMn2O4 or Li1.1Mn1.9O4
has good cycle life at room temperature, theses materials have a problem
of a rapid decrease in capacity upon continuous charge/discharge
operation at high temperature. In particular, dissolution of manganese
increases at a high temperature of 40° C. or more, causing rapid
deterioration in capacity (Electrochemical and Solid-State Letters, 8,
A171 (2005)). Although various attempts, such as substitution of a
fluorine atom into a oxygen site, have been made to solve the problem of
capacity deterioration caused by dissolution of manganese at high
temperature, the problem caused by the manganese dissolution has yet to
be overcome (Journal of Power sources, 81-82, 458 (1999)). In other
words, capacity deterioration caused by the manganese dissolution has not
solved yet, despite substitution of manganese using various elements (Mg,
Al, Co, Ni, Fe, Cr, Zn, Cu, etc.). (Journal of Power Sources, 68, 578
(1997); Journal of Power Sources, 68, 582 (1997); Solid State Ionics, 73,
233 (1994); Journal of Electrochemical Society, 143, 1607 (1996);
Proceeding of 11th International Conference on Solid State Ionics,
Honolulu, 1997, p. 23; Journal of Power Sources, 68, 604 (1997); Journal
of Solid State Chemistries, 132, 372 (1997); Solid State Ionics, 118, 179
(1999); Chemistry of Materials, 7, 379 (1995); Journal of Electrochemical
Society, 145, 1238 (1998); Materials Chemistry and Physics, 87, 162
(2004)); Journal of Power Sources, 102, 326 (2001))

[0009] Even in the case in which LiMn2O4 or
Li1.1Mn1.9O4 is formed through surface coating or complex
formation at a nanometer scale with stable MgO, Al2O3 and
Co3O4, capacity deterioration caused by dissolution of
manganese cannot be solved (Solid State Ionics, 167, 237 (2004);
Electrochem. Solid-State Lett. 5 A167 (2002); Chem. Commun. 2001, 1074).

[0010] Therefore, there is a need for a new spinel type anode active
material, which can suppress manganese dissolution in a spinel type
LiMn2O4 or Li1.1Mn1.9O4 and has stable cycle
lifespan at high temperature.

DISCLOSURE

Technical Problem

[0011] The present invention is directed to providing an anode active
material for rechargeable lithium batteries, in which spinel type
MgAl2O4 is substituted into a basic spinel structure
represented by Li1.1Mn1.9O4 to provide structural
stability and spinel type Co3O4 is substituted into the basic
spinel structure of Li1.1Mn1.9O4 to improve electronic
conductivity, thereby improving battery performance.

[0012] In addition, the present invention is directed to providing a
spinel type anode active material for rechargeable lithium batteries,
which has excellent lifespan characteristics by suppressing manganese
dissolution at high temperature.

Technical Solution

[0013] In accordance with one aspect of the present invention, an anode
active material for rechargeable lithium batteries includes a spinel type
anode active material
(Li1.1Mn1.9O4)1-x-y(MgAl2O4)x(Co3-
O4)y (0.001≦x≦0.2, 0.001≦y≦0.2),
which is formed by substituting spinel type (MgAl2O4)x and
spinel type (Co3O4)y into a basic spinel structure
represented by (Li1.1Mn1.9O4)1-x-y.

[0014] The spinel type anode active material may be mixed with metal oxide
nanoparticles MO (5 to 500 nm) (where M represents one of Mg, Co and Ni,
and has a valence of 2).

[0015] The metal oxide nanoparticles MO may act as scavengers of HF
generated by decomposition of an electrolyte.

[0016] The metal oxide nanoparticles may be mixed in an amount of 0.01 to
10% by weight (wt %) with the spinel type anode active material.

[0017] In accordance with another aspect of the present invention, a
method of preparing an anode active material for rechargeable lithium
batteries includes heat treating a mixture of Li2CO3,
MnO2, MgO, Al2O3 and Co3O4 at 900 to
1000° C. in air or an oxygen atmosphere for 10 to 48 hours to
generate a lithium-containing oxide; generating metal oxide nanoparticles
MO (5 to 500 nm) (where M represents one of Mg, Co and Ni, and has a
valence of 2); and dry or wet mixing 0.01 to 10 wt % of the pulverized
metal oxide nanoparticles with the lithium-containing oxide to form an
anode active material.

Advantageous Effects

[0018] As such, in the anode active material for rechargeable lithium
batteries according to the present invention, spinel type
MgAl2O4 is substituted into a basic spinel structure
represented by Li1.1Mn1.9O4 to provide structural
stability and spinel type Co3O4 is substituted into the basic
spinel structure of Li1.1Mn1.9O4 to improve electronic
conductivity, thereby improving battery performance.

[0019] In addition, according to the present invention, the spinel type
anode active material for rechargeable lithium batteries and the method
of manufacturing the same provide excellent lifespan characteristics by
suppressing manganese dissolution at high temperature as much as
possible. Specifically, hydrogen fluoride (HF) generated by decomposition
of an electrolyte salt easily dissolves manganese in the spinel
LiMn2O4. Thus, the content of hydrogen fluoride (HF) in the
electrolyte is lowered to suppress manganese dissolution as much as
possible by adding metal oxide nanoparticles MO (where M represents one
of Mg, Co and Ni, and has a valence of 2) having high electro negativity
in order to realize performance of the spinel anode active material, so
that the anode active material may achieve low price, high output, long
lifespan and high capacity of rechargeable lithium batteries, as compared
with the conventional anode active material.

DESCRIPTION OF DRAWINGS

[0020] FIG. 1 is a flowchart of a method of preparing an anode active
material for rechargeable lithium batteries in accordance with one
embodiment of the present invention;

[0032] Details of embodiments are included in the detailed description and
the accompanying drawings.

[0033] The above and other aspects, features, and advantages of the
invention will become apparent from the detailed description of the
following embodiments in conjunction with the accompanying drawings. It
should be understood that the present invention is not limited to the
following embodiments and may be embodied in different ways, and that the
embodiments are given to provide complete disclosure of the invention and
to provide a thorough understanding of the invention to those skilled in
the art. The scope of the invention is defined only by the claims. Like
components will be denoted by like reference numerals throughout the
specification.

[0034] Next, an anode active material for rechargeable lithium batteries
and a method of manufacturing the same according to exemplary embodiments
of the present invention will be described with reference to the
accompanying drawings.

[0035] An anode active material for rechargeable lithium batteries
according to one exemplary embodiment includes a spinel type anode active
material represented by
(Li1.1Mn1.9O4)1-x-y(MgAl2O4)x(Co3-
O4)y (0.001≦x≦0.2, 0.001≦y≦0.2),
which is formed by substituting spinel type (MgAl2O4)x and
spinel type (Co3O4)y into a basic spinel structure
represented by (Li1.1Mn1.9O4)1-x-y.

[0036] Specifically, in the anode active material for the rechargeable
lithium battery, thermodynamically stable MgO and Al2O3 are
converted into MgAl2O4 of a cubic spinel structure, which is
more thermodynamically stable than MgO and Al2O3, and
Co3O4 of a cubic spinel structure is substituted into the basic
spinel structure of Li1.1Mn1.9O4 to form the spinel type
anode active material represented by
(Li1.1Mn1.9O4)1-x-y(MgAl2O4)x(CO3-
O4)y (0.001≦x≦0.2, 0.001≦y≦0.2) in
order to enhance electronic conductivity, thereby providing structural
stability while improving battery performance.

[0037] Further, the spinel type anode active material may be mixed with
metal oxide nanoparticles MO (5 to 500 nm) (where M represents one of Mg,
Co and Ni, and has a valence of 2).

[0038] Here, the metal oxide nanoparticles MO provided as an additive act
as scavengers of HF generated by decomposition of an electrolyte.

[0039] Specifically, the metal oxide nanoparticles MO (5 to 500 nm) (where
M represents one of Mg, Co and Ni, and has a valence of 2) provided as an
additive act as scavengers of HF generated by decomposition of the
electrolyte, such that the spinel type anode active material may be used
as an anode active material of spinel type LiMn2O4 for
rechargeable lithium ion batteries, thereby realizing low price, high
output, long lifespan and high capacity of the rechargeable lithium
batteries.

[0040] Further, the metal oxide nanoparticles may be mixed in an amount of
0.01 to 10 wt % with the spinel type anode active material.

[0041] Next, referring to FIG. 1, a method of preparing an anode active
material for rechargeable lithium batteries according to one exemplary
embodiment will be described in detail.

[0042] The method of preparing an anode active material for rechargeable
lithium batteries includes heat treating a mixture of Li2CO3,
MnO2, MgO, Al2O3 and Co3O4 at 900 to
1000° C. in air or an oxygen atmosphere for 10 to 48 hours to
generate a lithium-containing oxide; generating metal oxide nanoparticles
MO (5 to 500 nm) (where M represents one of Mg, Co and Ni, and has a
valence of 2); and dry or wet mixing 0.01 to 10 wt % of the pulverized
metal oxide nanoparticles with the lithium-containing oxide to form an
anode active material.

[0043] Specifically, the anode active material for rechargeable lithium
batteries prepared by the method according to the embodiment is a spinel
type anode active material represented by
(Li1.1Mn1.9O4)1-x-y(MgAl2O4)x(Co3-
O4)y (0.001≦x≦0.2, 0.001≦y≦0.2),
which is formed by substituting spinel type (MgAl2O4) and
spinel type (Co3O4) into a basic spinel structure represented
by (Li1.1Mn1.9O4)1-x-y.

[0044] In the method according to this embodiment, first,
Li2CO3, MnO2, MgO, Al2O3, and Co3O4
are mixed in a predetermined ratio (in S100).

[0045] Here, Li2CO3, MnO2, MgO, Al2O3, and
Co3O4 are used as starting materials and may be prepared as
particles having a particle size of 20 micrometers or less in order to
generate a single phase.

[0046] Then, the mixture is subjected to heat treatment at 900 to
1000° C. in air or an oxygen atmosphere for 10 to 48 hours to
generate a lithium-containing oxide (in S200).

[0047] Here, although initial capacity increases with decreasing
calcination temperature, there is a problem of poor lifespan
characteristics in this case. As the calcination temperature increases,
the elution amount of manganese advantageously decreases due to a
decrease in specific surface area. Therefore, according to the present
invention, while a suitable calcination temperature for effectively
reducing the elution amount of manganese is maintained, thermodynamically
stable MgO and Al2O3 are converted into MgAl2O4 of a
cubic spinel structure, which is more thermodynamically stable than MgO
and Al2O3, and Co3O4 of a cubic spinel structure is
substituted into a basic spinel structure of Li1.1Mn1.9O4
to form a spinel type anode active material represented by
(Li1.1Mn1.9O4)1-x-y(MgAl2O4)x(Co3-
O4)y (0.001≦x≦0.2, 0.001≦y≦0.2) in
order to enhance electronic conductivity, thereby providing significantly
improved structural stability while enhancing electronic conductivity.

[0048] Then, metal oxide MO (where M represents one of Mg, Co and Ni, and
has a valence of 2) is pulverized to generate metal oxide nanoparticles
having a particle diameter of 5 to 500 nm (in S300).

[0049] Finally, the pulverized metal oxide nanoparticles are mixed in an
amount of 0.01 to 10 wt % with the lithium-containing oxide to form an
anode active material (in S400).

[0050] Herein, the "metal oxide nanoparticles" are prepared using an
electrochemically inactive metal oxide that has a different composition
than that of the anode active material for rechargeable lithium
batteries. When such metal oxide nanoparticles are uniformly dispersed
with the lithium-containing oxide for the anode active material, reaction
between the metal oxide nanoparticles and HF generated by decomposition
of an electrolyte salt predominantly occurs during charge/discharge
operation of the battery such that reaction between HF and the spinel
anode active material for rechargeable lithium batteries is suppressed,
thereby significantly improving a capacity maintaining rate of the anode
active material.

[0051] As for such metal oxide nanoparticles, metal oxide having high free
energy for formation and high electro negativity may be used.
Particularly, CoO, NiO, and MgO may be selectively used in various ways
according to characteristics of metal oxide.

[0052] As described above, the metal oxide nanoparticles are uniformly
mixed with the lithium-containing oxide for the anode active material
through dry or wet mixing.

[0053] Here, any typical dry or wet mixing process known in the art may be
used, without being limited to a particular process. For example, the
metal oxide nanoparticles may be mixed with a solvent having high
volatility under conditions suitably regulated according to the metal
oxide nanoparticles.

[0054] Here, the amount of the metal oxide nanoparticles may be suitably
regulated so as to improve electrochemical characteristics of the anode
active material. When the metal oxide nanoparticles are mixed in an
amount of 10 wt % or less, preferably 0.01 to 10 wt %, with the anode
active material, it is possible to prevent a reduction in the total
capacity of the battery.

[0055] If the amount of the metal oxide nanoparticles is less than 0.01 wt
%, the metal oxide nanoparticles do not provide sufficient effects. On
the contrary, if the amount of the metal oxide nanoparticles exceeds 10
wt %, the total capacity of the battery is reduced due to excess of the
metal oxide nanoparticles which are electrochemically inactive.

[0056] Meanwhile, an anode according to the present invention may be
manufactured using the anode active material through a known process.

[0057] For example, the anode active material is placed together with a
coupling agent such as polyvinylidone and a conductive agent such as
acetylene black, carbon black, and the like in an organic solvent such as
N-methyl-2-pyrrolidone to prepare a slurry composition for an anode
active material, which in turn is coated and dried on a current collector
such as an aluminum foil, thereby providing an anode.

[0058] Carbon or lithium is used as a cathode material. Then, a separator
is interposed between the cathode and the anode, which in turn are
inserted into a stainless steel and an aluminum pouch, or case
constituting an exterior member of a battery, followed by supplying a
liquid electrolyte and sealing to manufacture a rechargeable lithium
battery.

[0059] Next, X-ray diffraction patterns of anode active materials for
rechargeable lithium batteries according to one embodiment of the present
invention, which are represented by Li1.1Mn1.9O4 and
(Li1.1Mn1.9O4)1-x-y(MgAl2O4)x(Co3-
O4)y (x=0.025, y=0.05; x=0.2, y=0.2), will be described with
reference to FIG. 2.

[0060] Referring to FIG. 2, an upper part of the graph relates to
Li1.1Mn1.9O4, and a lower part of the graph relates to
(Li1.1Mn1.9O4)1-x-y(MgAl2O4)x(Co3-
O4)y (x=0.025, y=0.05; x=0.2, y=0.2), both of which have a
single phase spinel structure.

[0064] It can be seen that since Al (0.53 Å) and Co (0.535 Å) both
having relatively small ionic radii are substituted into sites of
Mn3+ (0.65 Å) having a relatively large ionic radius, the
lattice parameter is reduced.

[0065] In viewpoint of thermodynamics, thermodynamically stable MgO and
Al2O3 are converted into MgAl2O4 of a cubic spinel
structure, which is more thermodynamically stable than MgO and
Al2O3, and Co3O4 of a cubic spinel structure is
substituted into the basic spinel structure in order to enhance
electronic conductivity, thereby providing significantly improved
structural stability while enhancing electronic conductivity.

[0066] Next, initial discharge curves of half cells of
Li1.1Mn1.9O4 and
(Li1.1Mn1.9O4)1-x-y(MgAl2O4)x(Co3-
O4)y (x=0.025, y=0.05; x=0.2, y=0.2) will be described with
reference to FIG. 3.

[0067] Referring to FIG. 3, testing was performed under conditions wherein
an electric current was 100 mA/g (1 C) and operating temperature was
25° C., and Li1.1Mn1.9O4 had an inherent flat
voltage region of the spinel structure at 4V and a capacity of about 100
mAh/g.

[0068] Further, for
(Li1.1Mn1.9O4)1-x-y(MgAl2O4)x(CO3-
O4)y (x=0.025, y=0.05), since MgAl2O4 and
Co3O4 are substituted into some of electrochemically active
Mn3+ sites, electrochemical activity is reduced by the substituted amount
of Mn3+, causing a reduction of capacity to about 88 mAh/g. However,
lattice energy increases due to improvement of structural stability,
thereby enabling an increase in operating voltage in a zone of 4V or
more.

[0069] For (Li1.1Mn1.9O4)1-x-y(MgAl2O4)x(CO3O4)y (x=0.2, y=0.2), the discharge capacity was about
60 mAh/g.

[0070] Next, lifespan characteristics of Li1.1Mn1.9O4 and
(Li1.1Mn1.9O4)1-x-y(MgAl2O4)x(CO3-
O4)y (x=0.025, y=0.05; x=0.2, y=0.2) will be described with
reference to FIG. 4.

[0071] Referring to FIG. 4, testing was performed under conditions wherein
an applied current was 100 mA/g (1 C) and operating temperature was
60° C., spinel type Li1.1Mn1.9O4 underwent elution
of manganese from the active material to an electrolyte over repeated
cycling and such elution of Mn was accelerated at high temperature. This
phenomenon is caused by the following reaction:

2Mn3+→Mn2++Mn4+

[0072] In this reaction, Mn4+ couples with a lithium ion in the
electrolyte to form electrochemically inactive Li2MnO3, and
Mn2+ forms other complexities, which are attached to a cathode
surface and reduced into metal, causing an increase of cell resistance.

[0073] Accordingly, as can be seen in FIG. 4, the capacity is rapidly
reduced at 60° C. due to this reaction.

[0074] On the contrary, for a spinel type anode active material
represented by
(Li1.1Mn1.9O4)1-x-y(MgAl2O4)x(Co3-
O4)y (x=0.025, y=0.05), MgAl2O4 is substituted into
the structure of Li1.1Mn1.9O4, thereby further securing
structural stability, and Co3O4 is also substituted into the
structure of Li1.1Mn1.9O4, thereby further enhancing
electronic conductivity, so that the battery can maintain a capacity of
about 97% of an initial capacity thereof even after cycling at 60 to
100° C.

[0075] FIG. 5 is a transmission electron micrograph of CoO nanoparticles.
As can be seen from this transmission electron micrograph, CoO powder is
pulverized using a ball mill, thereby providing fine particles having a
particle size of 300 nm or less.

[0076] Next, an initial charge/discharge curve of a spinel electrode
including CoO nanoparticles in a half cell will be descried with
reference to FIG. 6.

[0077] Referring to FIG. 6, testing was performed under conditions wherein
an applied current was 100 mA/g (1 C) and operating temperature was
25° C. the spinel electrode including the CoO nanoparticles had a
high discharge voltage, causing resistance reduction and capacity
increase.

[0078] Therefore, it can be seen that the cell including the CoO
nanoparticles exhibits further improved characteristics of a half cell.

[0079] Next, cycling characteristics of the spinel electrode including CoO
nanoparticles in a half cell will be described with reference to FIG. 7.

[0080] Referring to FIG. 7, testing was performed under conditions wherein
an applied current was 100 mA/g (1 C) and operating temperature was
60° C., the spinel electrode including the CoO nanoparticles
exhibits further improved characteristics of a half cell even under high
temperature cycling at an operating temperature of 60° C.

[0081] Next, cycling characteristics of a spinel electrode including CoO
nanoparticles in a full cell will be described with reference to FIG. 8.

[0082] Referring to FIG. 8, testing was performed under conditions wherein
an applied current was 100 mA/g (1 C) and operating temperature was
60° C., the spinel electrode including the CoO nanoparticles
exhibits further improved characteristics of a full cell even in high
temperature cycling at an operating temperature of 60° C.

[0083] Particular, claim 10 of Patent Publication No. 2000-0029333 (May
25, 2000) discloses that cobalt oxide has a lattice parameter of
8.10±0.05 Å (space group Fd3m, cubic spinel). In this publication,
Co3O4 oxide coating is used as cobalt oxide of the cubic spinel
structure. According to the present invention, cobalt oxide (CoO, lattice
parameter a=4.26±0.05 Å) having a space group of Fm3m is used as
an additive.

[0084] The present invention is focused on the function of CoO capable of
scavenging HF. An electrolyte for lithium batteries contains about 50 ppm
or less of water (H2O). When reacting with water, electrolyte salt
LiPF6 is easily decomposed and such decomposition is accelerated
with increasing temperature (40 to 60° C.) causing the following
chemical reactions:

LiPF6→LiF↓+PF5 (1)

PF5+H2O→POF3+2HF (2)

2POF3+3Li2O→6LiF↓+P2O5↓ (or
LixPOFy) (3)

[0085] Then, HF continues to decompose the anode active material, thereby
causing severe elution of Mn through the following reaction.

[0087] On the other hand, as can be seen from FIGS. 7 and 8, the spinel
electrode including the CoO nanoparticles provides excellent cycling
characteristics upon charge/discharge operation. The reason for this
result is that the CoO nanoparticles react with HF generated by
decomposition of the electrolyte salt to scavenge HF according to the
following reaction.

[0089] As can be seen from FIG. 10, which shows the spectrum having a
relatively strong secondary ion fragment of CoF+ at a mass of 77.94,
CoO nanoparticles scavenged HF according to the above reaction formula
(5).

[0090] Generally, since CoO (ΔfG=-214 kJ/mol at 25° C.,
free energy of formation) is less stable than Co3O4
(ΔfG=-774 kJ/mol at 23'C), it is considered that CoO more
easily scavenges HF and is more effective than Co3O4.

[0091] Thus, as shown in FIG. 11, when observing
(Li1.1Mn1.9O4)1-x-y(MgAl2O4)x(CoO).sub-
.y (x=0.025, y=0.05, 10 wt % of CoO nanoparticles) powder using a
transmission electron micrograph (TEM) after cycling, it can be seen that
since CoO scavenges HF and prevents elution of Mn even after cycling, the
particle shape of the anode active material does not change as compared
with that of the anode active material before the charge/discharge
operation.

[0092] According to this result, it can be concluded that addition of the
metal oxide nanoparticles as in the present invention will lead to
further improvement of cell characteristics as compared with use of a
thin oxide coating.

[0093] As shown in FIG. 12, eluted manganese oxidizes into MnO and reacts
with HF, thereby generating a compound of MnF2 via the following
reaction.

MnO+2HF→MnF2+H2O (6)

[0094] As a result, it can be seen that the powder represented by
(Li1.1Mn1.9O4)1-x-y(MgAl2O4)x(CoO).sub-
.y (x=0.025, y=0.05, 10 wt % of CoO nanoparticles) effectively scavenges
HF, thereby significantly reducing elution of Mn as shown in FIG. 12.

[0095] From this result, it can be concluded that it is possible to
provide further improvement of the properties of the material using
functionality of the nanopowders.

[0096] Further, the anode active material for rechargeable lithium
batteries according to the present invention may be widely applied to
high performance rechargeable lithium batteries for mobile information
communication devices, such as mobile phones, PDAs (personal digital
assistants), MP3 players, camcorders, notebook computers, and the like,
and rechargeable batteries for high output large vehicles, such as
electric vehicles, hybrid electric vehicles (HEV) and the like.

[0097] Next, the present invention will be described with reference to
examples. Here, it should be understood that the following examples are
provided for illustration only and do not limit the scope of the present
invention.

[0099] These starting materials were placed in ethanol, followed by wet
mixing and drying at about 110° C. for 24 hours. Then, the mixture
was subjected to heat treatment at 500° C. for about 10 hours and
at 900 to 1000° C. in air or oxygen for 10 to 48 hours, thereby
preparing the anode material having the above composition.

Example 2

Preparation of Metal Oxide Nanoparticles

[0100] Cobalt oxide (CoO) powder was pulverized using a ball mill to a
particle size ranging from 5 to 500 nm. The pulverized nanoparticles were
heated to 80° C. to remove moisture therefrom.

Example 3

[0101] The prepared
(Li1.1Mn1.9O4)1-x-y(MgAl2O4)x(Co3-
O4)y (x=0.025, y=0.05) was uniformly mixed with the pulverized
cobalt oxide (CoO) nanoparticles in a weight ratio of 95:5.

[0102] The active material, polyvinylidene fluoride as a binder, and
carbon black as a conductive agent were dispersed in a weight ratio of
95:2:3 in NMP (N-methylpyrrolidone) to prepare a slurry. The slurry was
coated to a thickness of 100 micrometers on an Al foil using a doctor
blade, followed by evaporation of NMP at 120° C., pressing at a
predetermined pressure, and cutting to a predetermined size, thereby
preparing an anode plate.

[0103] As a cathode plate, a lithium foil was cut to the same size as the
anode plate, followed by a typical process for preparing a half cell.

[0104] Then, with a separator interposed between the cathode plate and the
anode plate, the resultant assembly was subjected to heating and
compression, and inserted into a coin cell provided as a battery case,
followed by injecting a liquid electrolyte and sealing the coin cell,
thereby providing a rechargeable lithium battery.

[0106] The prepared
(Li1.1Mn1.9O4)1-x-y(MgAl2O4)x(Co3-
O4)y (x=0.025, y=0.05) was uniformly mixed with the pulverized
cobalt oxide (CoO) nanoparticles in a weight ratio of 90:10. Then, the
battery was prepared by the same method as in Example 3.

Example 5

[0107] Synthetic graphite as a cathode active material and polyvinylidene
fluoride as a binder were dispersed in a weight ratio of 90:10 in NMP
(N-methylpyrrolidone) to prepare a slurry.

[0108] The slurry was coated to a thickness of 100 micrometers on an Al
foil using a doctor blade, followed by evaporation of NMP at 120°
C., pressing at a predetermined pressure, and cutting to a predetermined
size, thereby preparing a cathode plate.

[0109] The cathode plate was cut to the same size as the anode plate,
followed by a typical process for preparing a full cell. Then, with a
separator interposed between the anode plate and the cathode plate, the
resultant was subjected to heating and compression, and inserted into a
coin cell provided as a battery case, followed by injecting a liquid
electrolyte and sealing the coin cell, thereby providing a lithium ion
battery. The separator was obtained from Celgard Co., Ltd., and the
electrolyte was ethylene carbonate/diethyl carbonate (EC/DEC) containing
1 mole LiPF6.

[0110] The anode plates prepared in Examples 3 and 4 were used to prepare
full cells.

[0111] As starting materials, lithium carbonate (Li2CO3) and
manganese oxide (MnO2) were prepared. The anode active material had
a composition of (Li1.1Mn1.9O4). The starting materials
were placed in ethanol, followed by wet mixing and drying at about
110° C. for 24 hours. Then, the mixture was subjected to heat
treatment under the same conditions as those of Example 1, thereby
preparing a comparative material represented by
Li1.1Mn1.9O4.

Comparative Example 2

[0112] With this material, an anode plate and a half cell were prepared
under the same conditions as those of Example 3, and a cathode plate was
prepared under the same conditions as those of Example 5 to fabricate a
lithium ion battery.

[0114] A TEM image of metal oxide nanoparticles of Example 2 obtained
using TEM (Model No: H800, Hitachi, Japan) is shown in FIG. 5. It can be
ascertained that the pulverized metal oxide nanoparticles have a particle
size of 5 to 500 nm.

Experimental Example 3

Property Evaluation of Battery

[0115] For evaluation of properties of the lithium batteries prepared in
Examples 3 to 5 and Comparative Example 2, charge/discharge testing was
performed using a charge/discharge cycler (Model No. SM8, Hokuto Denko,
Japan) at 60° C. in a voltage range of 3.3 to 4.3 V at a current
density of 100 mA/g. The resultant charge/discharge curves are shown in
FIGS. 2, 3 and 6, and discharge capacity and efficiency are shown in
FIGS. 4, 7 and 8.

[0116] The examples according to the present invention exhibit superior
discharge capacity and cycling characteristics to those of the
comparative examples. In particular, as can be seen from FIGS. 7 and 8,
when 10 wt % of metal oxide (CoO) nanoparticles was added, the capacity
maintaining rate was significantly improved.

Experimental Example 4

TEM Measurement

[0117] The anode active material of Comparative Example 2 and the anode
active material of Example 5 were observed using TEM after cycling 100
times at 60° C. For the anode active material of Comparative
Example 2, the shape of the particles were significantly deteriorated due
to HF generated by decomposition of the electrolyte salt, whereas the
anode active material of Example 5 maintained particle shape thereof
through significant decrease in the amount of HF scavenged by CoO as
shown in FIG. 11.

[0119] As can be seen from FIG. 10, which shows the spectrum having a
relatively strong secondary ion fragment of CoF+ at a mass of 77.94,
CoO nanoparticles scavenged HF.

[0120] It can be seen that eluted manganese oxidizes into MnO and reacts
with HF, thereby generating MnF2, as shown in FIG. 12. As a result,
it can be ascertained that the powder represented by
(Li1.1Mn1.9O4)1-x-y(MgAl2O4)x(CoO).sub-
.y (x=0.025, y=0.05, 10 wt % of COO nanoparticles) effectively scavenges
HF, thereby significantly reducing elution of Mn as shown in FIG. 12.

[0121] From this result, it can be concluded that it is possible to
provide further improvement of the properties of the material using
functionality of the nanopowders.

[0122] Although some exemplary embodiments have been described with
reference to the accompanying drawings, it will be understood by those
skilled in the art that various modifications, changes, alterations, and
equivalent embodiments can be made without departing from the spirit and
scope of the invention. Therefore, it should be appreciated that the
foregoing embodiments are provided for illustrative purposes only and are
not to be in any way construed as limiting the present invention. The
scope of the present invention should be limited only by the accompanying
claims and equivalents thereof.